Endoprostheses

ABSTRACT

A hydrophilic ceramic coating is formed on an endoprosthesis preform. The hydrophilic ceramic coating is porous and can store nano-sized drug particles.

TECHNICAL FIELD

This invention relates to endoprostheses.

BACKGROUND

The body includes various passageways such as arteries, other blood vessels and other body lumens. These passageways sometimes become occluded or weakened. For example, the passageways can be occluded by a tumor, restricted by plaque, or weakened by an aneurysm. When this occurs, the passageway can be reopened or reinforced with a medical endoprosthesis. An endoprosthesis is typically a tubular member that is placed in a lumen in the body. Examples of endoprostheses include stents, covered stents, and stent-grafts.

Endoprostheses can be delivered inside the body by a catheter that supports the endoprosthesis in a compacted or reduced-size form as the endoprosthesis is transported to a desired site. Upon reaching the site, the endoprosthesis is expanded, e.g., so that it can contact the walls of the lumen. Stent delivery is further discussed in Heath, U.S. Pat. No. 6,290,721.

The expansion mechanism may include forcing the endoprosthesis to expand radially. For example, the expansion mechanism can include the catheter carrying a balloon, which carries a balloon-expandable endoprosthesis. The balloon can be inflated to deform and to fix the expanded endoprosthesis at a predetermined position in contact with the lumen wall. The balloon can then be deflated, and the catheter withdrawn from the lumen.

SUMMARY

In one aspect, the invention features an endoprosthesis that includes a preform. The preform includes a hydrophilic ceramic coating that has a contact angle of less than 30 degrees, for example, less than 5 degrees or less than 1 degree.

In another aspect, the invention features a method of making an endoprosthesis. The method includes (a) forming a ceramic coating on a perform and (b) treating the ceramic coating with a UV light.

In another aspect, the invention features a method of making an endoprosthesis that includes forming a hydrophilic ceramic coating having a contact angle of less than 30 degrees on a preform.

Embodiments may include any one or more of the following features. The hydrophilic ceramic coating can include pores. The pores can contain a hydrophilic therapeutic agent, for example, albumin coupled paclitaxel nanoparticles. The nanoparticles can have an average size of at least 100 nm, for example, about 130 nm. The hydrophilic ceramic coating can include titanium dioxide, rutile, anatase, or silicon dioxide.

Embodiments of the method of making an endoprosthesis may also include any one or more of the following features. The ceramic coating formed in step (a) can be hydrophobic and can have a contact angle greater than 90 degrees, and during step (b), at least a portion of, for example, the entire ceramic coating can be made less hydrophobic. The ceramic coating can be formed by depositing a sol gel solution on the preform, for example, using spin coating. The sol gel solution can include polyethylene glycol and a titanium dioxide precursor or silicon dioxide and a titanium dioxide precursor. The polyethylene glycol can have a molecular weight larger than 6000 and the precursor can include titanium alkoxide. The ceramic coating can include pores and step (a) can also include forming the pores by decomposing polyethylene glycol, by for example, calcination. The ceramic coating can be exposed to water vapor before step (b). The ceramic coating can include pores and step (b) can also include loading a therapeutic agent into the pores, for example, by dipping the preform in an aqueous solution that contains albumin paclitaxel nanoparticles. After step (b), the ceramic coating can be hydrophilic and can have a contact angle of at most 30 degrees.

Embodiments may include one or more of the following advantages. Stent can be formed with ceramic coatings that have pores and hydrophilicity properties that facilitates drug storage and eluting. In particular, a porous ceramic coating can be formed using a sol-gel process. The ceramic coating can have a good mechanical strength. The pores of the porous coating can be used to store drugs on the stent. The ceramic coating can include titanium dioxide and can be exposed to a low temperature water vapor to convert the titanium dioxide into an anatase or rutile state. The low temperature exposure can avoid destructions of polymers and/or drugs on the stent. A ceramic coating containing titanium dioxide in an anatase or rutile state can also be formed on the stent by physical vapor deposition. The ceramic coating can be photoactive and can be made hydrophilic upon exposure to UV illumination. The ceramic coating can be anti-microbial. The hydrophilic ceramic coating can facilitate absorption of hydrophilic drugs, for example, paclitaxel in the form of albumin-bound particle. More than one porous and hydrophilic ceramic coatings can be formed on the stent. Each ceramic coating can store a drug for eluting.

All publications, patent applications, patents, and other references mentioned herein are incorporated by reference herein in their entirety.

Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1A-1C are longitudinal cross-sectional views, illustrating delivery of a stent in a collapsed state, expansion of the stent, and deployment of the stent.

FIG. 2 is a perspective view of a fenestrated stent.

FIG. 3A is a cross-sectional view of a stent wall.

FIG. 3B is a photograph of a top view of the stent wall in FIG. 3A.

FIG. 3C is a perspective view of the stent wall in FIG. 3A.

FIG. 4 is a flow diagram, illustrating a method for making a stent of FIGS. 3A-3C.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIGS. 1A-1C, a stent 20 is placed over a balloon 12 carried near a distal end of a catheter 14, and is directed through the lumen 16 (FIG. 1A) until the portion carrying the balloon and stent reaches the region of an occlusion 18. The stent 20 is then radially expanded by inflating the balloon 12 and compressed against the vessel wall with the result that occlusion 18 is compressed, and the vessel wall surrounding it undergoes a radial expansion (FIG. 1B). The pressure is then released from the balloon and the catheter is withdrawn from the vessel (FIG. 1C).

Referring to FIG. 2, stent 20 includes a plurality of fenestrations 22 defined in a wall 23. Stent 20 includes several surface regions, including an outer, or abluminal, surface 24, an inner, luminal (or adluminal), surface 26, and a plurality of cutface surfaces 28. The stent can be balloon expandable, as illustrated above, or a self-expanding stent. Examples of stents are described in Heath, U.S. Pat. No. 6,290,721.

Referring to FIGS. 3A-3C, a stent wall 30 includes a stent body 32 and a ceramic coating 34. Ceramic coating 34 has pores 36 that contain a therapeutic agent 40.

In some embodiments, stent body 32 is formed, e.g., of a metallic material such as a metal, e.g. a metal alloy. Examples of the metallic material include 316L stainless steel, Co—Cr alloy, Nitinol, PERSS, MP35N, and other suitable metallic materials.

In some embodiments, ceramic coating 34 includes titanium dioxide (TiO₂) having a structure, e.g. of anatase or rutile. Ceramic coating 34 can also include vanadium oxide (V₂O₅), strontium titanate (SrTiO₃), potassium tantalate (KTaO₃), zirconia (ZrO₂), niobium oxide (Nb₂O₅), zinc oxide (ZnO), iron oxide (Fe₂O₃), or tungsten oxide (WO₃).

Coating 34 has a dendrite shape with dendrites 38 separated by pores 36. In some embodiments, dendrites 38 have an average length L of, for example, about 50 nm to about 500 nm and an average diameter D of, for example, about 50 nm to about 500 nm. Pores 36 has a depth similar to the length L of dendrite 38 and a diameter of, for example, about 10 nm to about 100 nm. TiO₂ is biocompatible and coating 34 can provide medical benefits. For example, TiO₂ can be treated to be highly anti-microbial, which is discussed in detail below. The biocompatibility of TiO₂ is also discussed in Tsyganov et al., Appl. Surf. Sci. 235, 156-163(2004). Coating 34 including vanadium oxide can include a porous nanostructure, for example, a roselike structure. Properties of vanadium oxide nanostructured coating is discussed in Lim et al., J. Am. Chem. Soc. 129, 4128-4129 (2007).

At least a portion of, for example, the entire, ceramic coating 34 is hydrophilic. For example, the contact angle of water droplets with ceramic coating 34, e.g., a surface of dendrites 38, can be less than, e.g., about 30 degrees, about 25 degrees, about 20 degrees, about 15 degrees, about 10 degrees, or about 8 degrees. In some embodiments, ceramic coating 34 is very hydrophilic and the contact angle of water droplets with ceramic coating 34 can be less than, e.g., about 5 degrees, about 3 degrees, about 1 degree, or about 0.5 degree.

In some embodiments, therapeutic agent 40 includes albumin coupled paclitaxel. The albumin coupled paclitaxel can be in the form of nano-particles having a size, e.g., of about 100 nm to about 200 nm, or 130 nm. These nano-particles are hydrophilic, allowing therapeutic agent 40 to have a full contact with the hydrophilic surface of dendrites 38 and readily fill pores 36.

In some embodiments, ceramic coating 34 also includes silicon dioxide (SiO₂). SiO₂ can increase the mechanical strength of dendrites 38 and thus allows coating 34 to be thick to provide a large dendrite height L and deep pores 36. A large amount of therapeutic agent 40 can be stored in coating 34.

Referring now to FIG. 4, an exemplary process including steps A-D for making a stent exemplified in FIGS. 3A-3C is illustrated.

Referring particularly to step A, coating 34 is formed by coating, e.g., spin-coating, TiO₂ on stent body 32 using a sol gel solution that contains a precursor, e.g., titanium alkoxide. The sol gel solution can also include polyethylene glycol (PEG). In some embodiments, the PEG in the sol gel solution has a molecular weight, for example, of at least about 5000 or about 6000, and/or up to, for example, about 15000 or about 20000. The PEG molecules can reduce cracks in coating 34. In some embodiments, coating 34 is crack free. Coating 34 is then calcinated, e.g., at about 400° C. or higher, or about 550° C. or higher, and TiO₂ is crystallized to have a anatase or rutile structure. During the calcination, the PEG molecules decompose and create pores 36 in the TiO₂ coating. The density and size of pores 36 can be controlled by controlling the number and molecular weight of the PEG molecules added in the coating 34. For example, a larger number of the PEG molecules leads to a larger pore density and larger molecular weight PEG molecules create larger sized pores.

In some embodiments, coating 34 that includes TiO₂ having an anatase or rutile structure can also be prepared by exposing sol-gel-derived TiO₂ and sol-gel-derived silica (SiO₂) to water vapor. A sol gel solution containing a TiO₂ precursor, e.g., titanium tetraisopropoxide, and a SiO₂ precursor, e.g., silicon tetraethoxide is coated on stent body 32. The coating is subsequently dried, for example, at 60° C., and exposed to water vapor that has a relative humidity, for example, of 100%, at a relatively low temperature, for example, of about 60° C. to about 180° C. (e.g. 90° C.). So-formed coating 34 includes about 0 to 50 mol % of SiO₂ and crystalline TiO₂ that has an anatase or rutile structure. The SiO₂ included in the coating facilitates the crystallization of TiO₂ when the coating is exposed to the water vapor. In addition, the SiO₂ also enhances the adhesion and mechanical strength of the coating on the stent body. In some embodiments, TiO₂ and SiO₂ have different phases and the separation of these phases creates pores 36 in coating 34. The density and sizes of the pores 36 can be controlled by controlling the amount of SiO₂ included in coating 34 and/or the temperature of the water vapor. The relatively low working temperature of the water vapor process allows the inclusion of polymers and therapeutic agents during or before the water vapor process. Sol gel process is also discussed in Guo et al., surface & Coatings Technology 198, 24-29 (2005); Imai et al., J. American Ceramic Society 82, 2301-2304 (1999); U.S. Ser. No. 61/073,647, filed on Jun. 18, 2008; and U.S. Ser. No. 61/056,912, filed on May 29, 2008.

Referring to step B, at least a portion of, for example, the entire, coating 34 is exposed to an ultraviolet (UV) light radiation, for example, for about 1 hour. The portions of coating 34 that are not preferred to be exposed to the UV light can be covered, for example, by a UV resistant cover. UV light, as used herein, is defined to be electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. For example, the UV light can have a wavelength of about 156 nm to about 400 nm, e.g., 365 nm or 193 nm. The incident photon in the UV light induces the photo-catalytic effects of anatase or rutile structured TiO₂ and coating 34 becomes hydrophilic or super-hydrophilic. The UV light and the photo-catalytic effect can also sterilize coating 34. For example, when photons of UV-A light are absorbed by the ceramic, e.g., titanium dioxide, pairs of electrons and holes are generated. The photogenerated holes react with water to produce hydroxyl radicals (.OH) and the photogenerated electrons react with molecular oxygen to produce superoxide radical anions (.O2). The hydroxyl radicals and the superoxide radical anions are highly reactive and can oxidize and thus destroy organic species, for example, bacteria, in coating 34. Information about photo-catalytic effects and super-hydrophilicity of the TiO₂ coating is also provided in Yu et al., J. Photochemistry and Photobiology A: Chemistry 148, 331-339 (2002); Karuppuchamy et al., Materials Chemistry and Physics 93, 251-254 (2005); Zhong et al., Appl. Phys. Lett. 85, 5067-5069 (2004).

Referring to step C, therapeutic agent 40 is filled into pores 36 by dipping stent wall 30 into an aqueous solution. The aqueous solution contains therapeutic agent 40, for example, hydrophilic albumin paclitaxel or Abraxane® (ABI-007). The albumin paclitaxel are in the form of nanoparticles that have a size smaller than the pores of the TiO₂ coating. When in contact with the hydrophilic coating 34, the nanoparticles are sucked into pores 36 and fill up the pores. The hydrophilicity of both the TiO₂ coating and the albumin paclitaxel nanoparticles enables an easy drug loading to the stent and also allows a large amount of the drug to be loaded in the pores. The stent is subsequently dried, for example, at 90° C.

Referring to step D, optionally, another coating that includes TiO₂ and contains a therapeutic agent can be formed by repeating the steps A-C on coating 34. Particularly, in step A of forming the second coating, the low temperature process of exposing sol-gel-derived TiO₂ and sol-gel-derived silica (SiO₂) to water vapor is preferred so that therapeutic agent 40 in coating 34 is not affected by these successive processes.

The terms “therapeutic agent,” “pharmaceutically active agent,” “pharmaceutically active material,” “pharmaceutically active ingredient,” “drug” and other related terms may be used interchangeably herein and include, but are not limited to, small organic molecules, peptides, oligopeptides, proteins, nucleic acids, oligonucleotides, genetic therapeutic agents, non-genetic therapeutic agents, vectors for delivery of genetic therapeutic agents, cells, and therapeutic agents identified as candidates for vascular treatment regimens, for example, as agents that reduce or inhibit restenosis. By small organic molecule is meant an organic molecule having 50 or fewer carbon atoms, and fewer than 100 non-hydrogen atoms in total.

Exemplary therapeutic agents include, e.g., anti-thrombogenic agents (e.g., heparin); anti-proliferative/anti-mitotic agents (e.g., paclitaxel, 5-fluorouracil, cisplatin, vinblastine, vincristine, inhibitors of smooth muscle cell proliferation (e.g., monoclonal antibodies), and thymidine kinase inhibitors); antioxidants; anti-inflammatory agents (e.g., dexamethasone, prednisolone, corticosterone); anesthetic agents (e.g., lidocaine, bupivacaine and ropivacaine); anti-coagulants; antibiotics (e.g., erythromycin, triclosan, cephalosporins, and aminoglycosides); agents that stimulate endothelial cell growth and/or attachment. Therapeutic agents can be nonionic, or they can be anionic and/or cationic in nature. Therapeutic agents can be used singularly, or in combination. Preferred therapeutic agents include inhibitors of restenosis (e.g., paclitaxel), anti-proliferative agents (e.g., cisplatin), and antibiotics (e.g., erythromycin). Additional examples of therapeutic agents are described in U.S. Published Patent Application No. 2005/0216074. In embodiments, the drug can be incorporated within the porous regions in a polymer coating. Polymers for drug elution coatings are also disclosed in U.S. Published Patent Application No. 2005/019265A. A functional molecule, e.g., an organic, drug, polymer, protein, DNA, and similar material can be incorporated into grooves, pits, void spaces, and other features of the stent.

Suitable polymers include, for example, polycarboxylic acids, cellulosic polymers, including cellulose acetate and cellulose nitrate, gelatin, polyvinylpyrrolidone, cross-linked polyvinylpyrrolidone, polyanhydrides including maleic anhydride polymers, polyamides, polyvinyl alcohols, copolymers of vinyl monomers such as EVA, polyvinyl ethers, polyvinyl aromatics such as polystyrene and copolymers thereof with other vinyl monomers such as isobutylene, isoprene and butadiene, for example, styrene-isobutylene-styrene (SIBS), styrene-isoprene-styrene (SIS) copolymers, styrene-butadiene-styrene (SBS) copolymers, polyethylene oxides, glycosaminoglycans, polysaccharides, polyesters including polyethylene terephthalate, polyacrylamides, polyethers, polyether sulfone, polycarbonate, polyalkylenes including polypropylene, polyethylene and high molecular weight polyethylene, halogenerated polyalkylenes including polytetrafluoroethylene, natural and synthetic rubbers including polyisoprene, polybutadiene, polyisobutylene and copolymers thereof with other vinyl monomers such as styrene, polyurethanes, polyorthoesters, proteins, polypeptides, silicones, siloxane polymers, polylactic acid, polyglycolic acid, polycaprolactone, polyhydroxybutyrate valerate and blends and copolymers thereof as well as other biodegradable, bioabsorbable and biostable polymers and copolymers. Coatings from polymer dispersions such as polyurethane dispersions (BAYHDROL®, etc.) and acrylic latex dispersions are also within the scope of the present invention. The polymer may be a protein polymer, fibrin, collagen and derivatives thereof, polysaccharides such as celluloses, starches, dextrans, alginates and derivatives of these polysaccharides, an extracellular matrix component, hyaluronic acid, or another biologic agent or a suitable mixture of any of these, for example. In one embodiment, the preferred polymer is polyacrylic acid, available as HYDROPLUS® (Boston Scientific Corporation, Natick, Mass.), and described in U.S. Pat. No. 5,091,205, the disclosure of which is hereby incorporated herein by reference. U.S. Pat. 5,091,205 describes medical devices coated with one or more polyiocyanates such that the devices become instantly lubricious when exposed to body fluids. In another preferred embodiment of the invention, the polymer is a copolymer of polylactic acid and polycaprolactone. Suitable polymers are discussed in U.S. Publication No. 2006/0038027.

In embodiments, the polymer is capable of absorbing a substantial amount of drug solution. When applied as a coating on a medical device in accordance with the present invention, the dry polymer is typically on the order of from about 1 to about 50 microns thick. Very thin polymer coatings, e.g., of about 0.2-0.3 microns and much thicker coatings, e.g., more than 10 microns, are also possible. Multiple layers of polymer coating can be provided. Such multiple layers are of the same or different polymer materials.

Any stent described herein can be dyed or rendered radiopaque by addition of, e.g., radiopaque materials such as barium sulfate, platinum or gold, or by coating with a radiopaque material. The stent can include (e.g., be manufactured from) metallic materials, such as stainless steel (e.g., 316L, BioDur® 108 (UNS S29108), and 304L stainless steel, and an alloy including stainless steel and 5-60% by weight of one or more radiopaque elements (e.g., Pt, Ir, Au, W) (PERSS®) as described in US-2003-0018380-A1, US-2002-0144757-A1, and US-2003-0077200-A1), Nitinol (a nickel-titanium alloy), cobalt alloys such as Elgiloy, L605 alloys, MP35N, titanium, titanium alloys (e.g., Ti-6A1-4V, Ti-50Ta, Ti-10Ir), platinum, platinum alloys, niobium, niobium alloys (e.g., Nb-1Zr) Co-28Cr-6Mo, tantalum, and tantalum alloys. Other examples of materials are described in commonly assigned U.S. application Ser. No. 10/672,891, filed Sep. 26, 2003; and U.S. application Ser. No. 11/035,316, filed Jan. 3, 2005. Other materials include elastic biocompatible metal such as a superelastic or pseudo-elastic metal alloy, as described, for example, in Schetsky, L. McDonald, “Shape Memory Alloys”, Encyclopedia of Chemical Technology (3rd ed.), John Wiley & Sons, 1982, vol. 20. pp. 726-736; and commonly assigned U.S. application Ser. No. 10/346,487, filed Jan. 17, 2003.

The stents described herein can be configured for vascular, e.g., coronary and peripheral vasculature or non-vascular lumens. For example, they can be configured for use in the esophagus or the prostate. Other lumens include biliary lumens, hepatic lumens, pancreatic lumens, urethral lumens.

The stent can be of a desired shape and size (e.g., coronary stents, aortic stents, peripheral vascular stents, gastrointestinal stents, urology stents, tracheal/bronchial stents, and neurology stents). Depending on the application, the stent can have a diameter of between, e.g., about 1 mm to about 46 mm. In certain embodiments, a coronary stent can have an expanded diameter of from about 2 mm to about 6 mm. In some embodiments, a peripheral stent can have an expanded diameter of from about 4 mm to about 24 mm. In certain embodiments, a gastrointestinal and/or urology stent can have an expanded diameter of from about 6 mm to about 30 mm. In some embodiments, a neurology stent can have an expanded diameter of from about 1 mm to about 12 mm. An abdominal aortic aneurysm (AAA) stent and a thoracic aortic aneurysm (TAA) stent can have a diameter from about 20 mm to about 46 mm. The stent can be balloon-expandable, self-expandable, or a combination of both (e.g., see U.S. Pat. No. 6,290,721).

Other embodiments are in the following claims. 

1. A method of making an endoprosthesis, comprising: (a) depositing a sol gel solution including a titanium dioxide precursor and a polymer to form a ceramic coating on a preform, the polymer comprising polyethylene glycol having a molecular weight larger than 6000, and the titanium oxide precursor comprising titanium alkoxide; and (b) treating the ceramic coating with a UV light.
 2. The method of claim 1, wherein the ceramic coating formed in step (a) is hydrophobic and has a contact angle greater than 90°, and during step (b), at least a portion of the ceramic coating is made less hydrophobic.
 3. The method of claim 1, comprising depositing the sol gel solution by spin coating.
 4. The method of claim 1, wherein the ceramic coating comprises pores and step (a) further comprises forming the pores by decomposing polyethylene glycol.
 5. The method of claim 4, comprising decomposing polyethylene glycol by calcination.
 6. The method of claim 1, further comprising exposing the ceramic coating to water vapor before step (b).
 7. The method of claim 1, wherein the ceramic coating includes pores and step (b) further comprises loading a therapeutic agent into the pores.
 8. The method of claim 7, comprising loading the therapeutic agent by dipping the preform in an aqueous solution containing albumin paclitaxcel nanoparticles.
 9. The method of claim 1, wherein after step (b), the ceramic coating is hydrophilic and has a contact angle of at most 30 degrees.
 10. The method of claim 1, wherein the ceramic coating comprises silicon dioxide.
 11. The method of claim 10, wherein the ceramic coating comprises 0-50 mol % of silicon dioxide.
 12. The method of claim 10, wherein step (a) further comprises separating phases of the silicon dioxide and titanium dioxide in the ceramic coating to form pores in the ceramic coating.
 13. The method of claim 6, wherein the water vapor has a temperature of about 60° C. to about 180° C.
 14. The method of claim 7, wherein the therapeutic agent is in the form of nanoparticles. 